<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        html,body{
            width: 100%;
            height: 100%;
        }
        .root{
            width: 100%;
            height: 100%;
            display: flex;
            justify-content: center;
        }
        .App{
            width: 40%;
            border: 1px solid gray;
            display: flex;
            flex-direction: column;
            align-items: center;
        }
        .App>.header{
            width: 80%;
            height: 30px;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        .search{
            width: 80%;
            height: 80%;
        }
        .search:active{
            box-shadow: 2px 2px 10px bisque;
        }

        .content{
            height: 30px;
            width: 80%;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        ul{
            list-style: none;
        }
        ul>li{
            display: flex;
            width: 100%;
            height: 20px;
        }
        ul>li:hover>button{
            background-color: red;
            color: white;
            display: block;
        }
        ul>li>button{
            display: none;
        }
    </style>
</head>
<body>
    <div class="root">
        <div class="App">
            <div class="header">
                <input type="text" placeholder='请输入内容...' class="search">
            </div>
            <div class="content">
                <ul>
                    <li>
                        <input type="checkbox"/>
                        内容部分
                        <button>删除</button>
                    </li>
                </ul>
            </div>
            <div class="footer">
                <input type="checkbox"/>已完成: 0 / 总计: 3 <button>删除所有</button>
            </div>
        </div>
    </div>
</body>
</html>